One thing is certain: today is the first day of two thousand ten (or is it twenty ten?). Be that as it may, the media universally have been celebrating the end of a decade, variously described as the noughts or the first decade of the twenty-first century. Most of us are indeed eager to put the past 10 years behind us, a period of our history tainted by terrorism, endless (and often pointless) war, and bitter partisanship unconcerned with either democracy or the common good. A lesson about decades is in order, however.
We are used to speaking of the 80s or 90s, by which we mean the periods 1980–1989 or 1990–1999, respectively. They represent 10-year intervals and can properly be called decades. The years 2000–2009 presented a problem, however. By analogy, these years should have been the 00s. How does one pronounce that? Of course, we also spoke of the 1980s or 1990s, and the analogy here, 2000s, works a little better, though context is needed to distinguish between a reference to a decade and one to a century. (Most people would now construe 1900s as a reference to a century.)
The period 1900–1909 was, apparently, referred to as the noughts, referring to the zero or nought in the third digit of each of the included years. Thus, many have referred to the 2000–2009 decade as the noughts. Since naught or aught can also mean zero, we can also properly speak of the naughts or aughts. Rather rarely is ought used to mean zero—the usage is not unheard of—so I view use of the oughts (here, for example) as something of an illiteracy. (This latter usage is too easily confused with obligations.)
Logically, the years 2010–2019 present us with another linguistic problem. Inevitably, I suppose, this decade will be called the teens, and we are unlikely to see them referred to as the 10s or the the 2010s. Strictly speaking, however, only the numbers 13–19 are teens. (A twelve-year-old is not considered a teenager.) The teens is a bit of a misnomer, but one we are likely to live with.
Of course, those people saying goodbye to the first decade of the twenty-first century are simply celebrating a year too early. The first decade of the twenty-first century comprises the years 2001–2010. There was no year 0, so the first decade of the first century comprised the years 1–10. This means that the twentieth century ended in 2000, not in 1999. Nobody seems to remember that.